UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United StatesDepartment of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Matthew C. Murphy

UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Jasmine Kashkoush

UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Amy C. Nau

UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Purpose :
Visual cortex functionality in the blind has been shown to shift away from sensory networks toward task-positive networks that are involved in top-down modulation. However, how such modulation is shaped by experience and reflected behaviorally remains unclear. This study evaluated the training-induced top-down visual cortex activity as a function of blindness duration or behavioral response using blood-oxygen-level-dependent (BOLD) functional MRI (fMRI) with a sensory substitution task.

Methods :
Four congenitally blind subjects (age= 50.8±17.5 years), 7 acquired blind subjects (age= 45.4±16.6 years) and 11 sighted controls (age= 49.9±16.2 years) underwent task-based fMRI at 3 Tesla. Subjects were asked to interpret a series of vOICe soundscapes that represented moving bars across an image in different directions before and after sensory substitution training in the scanner. BOLD % change representing the strength of functional response was extracted from 3 regions of interest including primary, secondary and tertiary visual cortices. To determine the degree of top-down modulation in the visual cortex, we subtracted the pre-training BOLD% change from the post-training BOLD% change (ΔBOLD%) for each of the 3 ROIs in each subject. The relationships between ΔBOLD% and duration of blindness or behavioral reaction time were then tested by non-parametric Spearman correlations.

Results :
Both blind groups but not the sighted group showed increased positive BOLD responses in the visual cortex after training, indicating increased top-down modulation of the visual cortex in the blind but not sighted subjects (Fig 1). When evaluating the degree of top-down brain modulation, our further analyses showed a decreasing BOLD activity change in the primary visual cortex of acquired blindness with increasing blindness duration (Fig 2a). The degree of top-down modulation in primary visual cortex also negatively correlated with reaction time during sensory substitution (Fig 2b).

Conclusions :
Our results showing decreasing top-down activity in the visual cortex of subjects with acquired blindness over time indicated that the plasticity of the visual system can gradually be reshaped after late onset of blindness beyond the sensitive period. Furthermore, the degree of top-down activity in the visual cortex may influence the speed of performance during sensory substitution tasks.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.